A conventional bipolar transistor in a BiCMOS process adopts heavily doped collector region buried layers to reduce the collector region resistance. The collector region buried layers are connected by N-type implantation with high concentration and high energy so as to form a collector pick-up. Medium to lightly doped collector regions are formed on the collector region buried layers by epitaxy. A base region is formed by in-situ P-doped epitaxy, and an emitter region is formed by N-type heavily-doped polysilicon. Thereby, a bipolar transistor is fabricated.